The invention pertains to transport refrigeration systems and in particular to an air flow system for a refrigerated container such as a refrigerated trailer with a forced convection heat transfer system.
It is important that the air circulation within such containers be adequate for several reasons. Air should be delivered throughout the load and wipe the interior walls and floors to accomplish the required heat transfer to maintain trailer and load temperature at the proper level. The air delivered through the evaporator coil should be adequate to transfer heat without excessive temperature differences in the air. With highly restricted air circulation, the air temperature leaving the evaporator will be very low for loads being cooled and very high for loads requiring heating. In either case, the commodity being carried within the trailer can suffer from overheating or overcooling. If there is a reduced air flow the velocity from the evaporator air outlet is reduced, which in turn reduces the throw of air toward the rear of the trailer.
It is known that for reasons of overall economy the users of trailers wish to maximize the volume within the trailer, which tends to minimize the space available for air flow. It is also known that for structural and economy reasons, many trailers are constructed with a corrugated duct board type of floor which is known to be less desirable for return air flow under the load to the refrigeration unit than the so-called high profile T section type of floor.
In virtually all cases it is desirable that an adequate quantity of air reach the rear portion of the trailer. One way of doing this is to use a longitudinally extending duct along the centered ceiling of the trailer and connecting it to the outlet of the refrigeration unit. Some objections to this centered duct system is that the ducts are subject to being easily damaged by fork trucks, are unsanitary, and expensive to maintain. Other arrangements for improving air circulation and air temperature control are Venturi-type devices associated with the outlet of the transport refrigeration unit and are exemplified by U.S. Pat. Nos. 3,792,595, 3,447,336 and 2,780,923. Such devices are also subject to being easily damaged and do not assure that an adequate quantity of air will reach the rear of the trailer.
The aim of this invention is to provide an air flow system which operates to assure a supply of air to the rear portion of the trailer and to assure a return of air to the unit, irrespective of severe restrictions in the conventional return air path to the refrigeration unit, so that at all times there is adequate air flow through the unit evaporator coil and thus extreme temperature differences across the coil are avoided.